Skew-tolerant reader set selection in array-reader based magnetic recording

ABSTRACT

A method for enhancing read performance in an ARMR system includes: obtaining CTS information for a plurality of readers in a multi-reader head of the ARMR system, the CTS information defining a relationship between skew angle and CTS between respective combinations of subsets of the readers; determining, as a function of the CTS information, a given one of the combinations of subsets of the readers which provides enhanced read performance among a total number of combinations of subsets of the readers for each of a plurality of skew angles; and selecting, for subsequent processing by a read channel in the ARMR system, the given one of the combinations of subsets of the readers determined to provide enhanced read performance for a given one of the skew angles corresponding to a zone in which the multi-reader head is operating.

FIELD OF INVENTION

The present invention relates generally to electrical and electronic circuitry, and more particularly relates to magnetic recording.

BACKGROUND

The magnetic disk drive recording industry continues to pursue advances in technology that will sustain enhancements in recording density in a cost-effective manner. Two approaches currently under investigation are bit patterned media recording (BPMR) and heat-assisted magnetic recording (HAMR). An objective of these approaches is to overcome challenges posed by the super-paramagnetic limit that imposes a trade-off among three fundamentally competing recording parameters: media signal-to-noise ratio (SNR), writability and thermal stability. BPMR and HAMR, however, require modifications to the media and heads which significantly increase costs. Another technology, two-dimensional magnetic recording (TDMR), which uses conventional media and a new multiple-head configuration, relies on powerful signal processing in an attempt to achieve a theoretical one bit-per-grain recording density.

As a practical near-term milestone, array-reader based magnetic recording (ARMR) has been proposed to increase areal density with an array-reader and associated signal processing.

SUMMARY

In accordance with an embodiment of the invention, a method for enhancing read performance in an ARMR system includes: obtaining cross-track separation (CTS) information for a plurality of readers in a multi-reader head of the ARMR system, the CTS information defining a relationship between skew angle and CTS between respective combinations of subsets of the readers; determining, as a function of the CTS information, a given one of the combinations of subsets of the readers which provides enhanced read performance among a total number of combinations of subsets of the readers for each of a plurality of skew angles; and selecting, for subsequent processing by a read channel in the ARMR system, the given one of the combinations of subsets of the readers determined to provide enhanced read performance for a given one of the skew angles corresponding to a zone in which the multi-reader head is operating. Other embodiments of the invention include but are not limited to being manifest as an ARMR system, a data storage system, and an integrated circuit including at least a portion of an ARMR system. Additional and/or other embodiments of the invention are described in the following written description, including the claims, which is to be read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings are presented by way of example only and without limitation, wherein like reference numerals (when used) indicate corresponding elements throughout the several views, and wherein:

FIG. 1 is a block diagram depicting at least a portion of a magnetic disk drive storage system in which one or more embodiments of the invention are employed;

FIG. 2 is a block diagram depicting at least a portion of read-back signal processing blocks for an exemplary two-reader ARMR system;

FIGS. 3A-3C are top plan views conceptually depicting how reader cross-track separation varies with skew angle for an exemplary multi-reader head;

FIG. 4 is a top plan view depicting a two-reader head in various cross-track separation, down-track separation and skew angle configurations relative to corresponding tracks in an ARMR system;

FIG. 5 is a top plan view depicting exemplary configurations of a read head comprising three readers in a zero-skew position relative to a corresponding magnetic storage medium, according to one or more embodiments of the invention;

FIG. 6 conceptually depicts an illustrative methodology for selecting a combination of readers as a function of skew angle given a first exemplary placement of readers in a multi-reader head configured for multiple-input single-output (MISO) operation, according to an embodiment of the invention;

FIG. 7 conceptually depicts an illustrative methodology for selecting a combination of readers as a function of skew angle given a second exemplary placement of readers in a multi-reader head configured for MISO operation, according to an embodiment of the invention;

FIG. 8 conceptually depicts an illustrative methodology for selecting a combination of readers as a function of skew angle given a third exemplary placement of readers in a multi-reader head configured for MISO operation, according to an embodiment of the invention;

FIG. 9 conceptually depicts an illustrative methodology for selecting a combination of readers as a function of skew angle given a first exemplary placement of readers in a multi-reader head configured for multiple-input multiple-output (MIMO) operation, according to an embodiment of the invention;

FIG. 10 conceptually depicts an illustrative methodology for selecting a combination of readers as a function of skew angle given a second exemplary placement of readers in a multi-reader head configured for MIMO operation, according to an embodiment of the invention;

FIG. 11 conceptually depicts an illustrative methodology for selecting a combination of readers as a function of skew angle given a third exemplary placement of readers in a multi-reader head configured for MIMO operation, according to an embodiment of the invention;

FIG. 12 is a top plan view depicting exemplary configurations of a read head comprising four readers in a zero-skew position relative to a corresponding magnetic storage medium, according to one or more embodiments of the invention;

FIG. 13 is a block diagram depicting at least a portion of an exemplary read channel in which one or more embodiments of the invention are employed that is suitable for use in an ARMR system, according to an embodiment of the invention;

FIG. 14 depicts a computer system that may be useful in implementing one or more embodiments and/or elements of the invention; and

FIG. 15 is a block diagram depicting at least a portion of an exemplary virtual storage system comprising multiple storage devices, at least one of the storage devices incorporating techniques for enhancing skew tolerance in a multi-reader ARMR environment, according to an embodiment of the invention.

It is to be appreciated that the drawings described herein are presented for illustrative purposes only. Moreover, common but well-understood elements and/or features that may be useful or necessary in a commercially feasible embodiment may not be shown in order to facilitate a less hindered view of the illustrated embodiments.

WRITTEN DESCRIPTION

Embodiments of the invention will be described herein in the context of illustrative array-reader based magnetic recording (ARMR) systems for use, for example, in a data storage application. It should be understood, however, that embodiments of the invention are not limited to these or any other particular ARMR arrangements. Rather, embodiments of the invention are more broadly applicable to techniques for improving read performance of a magnetic storage device. In this regard, embodiments of the invention provide an apparatus and methodology for beneficially mitigating the impact of skew in an ARMR system. More particularly, one or more embodiments of the invention utilize a greater number of readers than read channels and select a subset of the readers, based at least in part on skew-dependent (or zone-dependent) cross-track separation (CTS) evaluation, which provides enhanced read performance to thereby improve skew tolerance in the ARMR system. Moreover, it will become apparent to those skilled in the art given the teachings herein that numerous modifications can be made to the illustrative embodiments shown that are within the scope of the claimed invention. That is, no limitations with respect to the embodiments shown and described herein are intended or should be inferred.

As a preliminary matter, for purposes of clarifying and describing embodiments of the invention, the following table provides a summary of certain acronyms and their corresponding definitions, as the terms are used herein:

Table of Acronym Definitions Acronym Definition BPMR Bit patterned media recording HAMR Heat-assisted magnetic recording SNR Signal-to-noise ratio TDMR Two-dimensional magnetic recording ARMR Array-reader based magnetic recording MISO Multiple-input single-output MIMO Multiple-input multiple-output CTS Cross-track separation VCM Voice coil motor CPU Central processing unit SSD Solid-state drive RAM Random access memory PMR Perpendicular magnetic recording ITI Inter-track interference TP Track pitch BL Bit length BAR Bit aspect ratio RW Reader width AFE Analog front end DTS Down-track separation OD Outer diameter MD Mid-diameter ID Inner diameter OTER On-track error rate OTC Off-track capability MD Mid-diameter BER Bit error rate

FIG. 1 is a block diagram depicting at least a portion of an exemplary data storage system 100 in which one or more embodiments of the invention are employed. The storage system 100 includes a read/write channel 102 having reader set selection circuitry in accordance with embodiments of the invention, a preamplifier (preamp) 104 coupled with the read/write channel, an interface controller 106 coupled with the read/write channel, a hard disk controller 110 coupled with the interface controller, a motor controller 112 coupled with the hard disk controller, and a spindle motor 114 coupled with and operative to rotate a disk platter 116 comprising a plurality of tracks, or an alternative magnetic storage medium. A voice coil motor (VCM) 118 attached to an actuator arm is configured to maintain a position of at least one read/write head 120 above a surface of the disk platter 116 as a function of one or more control signals generated by the motor controller 112. In a multi-reader configuration, the system 100 would include multiple read/write heads and corresponding preamplifiers coupled therewith. Thus, read/write head 120 is intended to collectively represent one or a plurality of read/write heads; likewise, preamplifier 104 is intended to collectively represent one or a plurality of preamplifiers coupled with corresponding read/write heads.

The read/write channel 102 is the fundamental mixed signal analog/digital module of the disk drive storage system 100 and, although shown as a single block, is actually comprised of two separate channels: a read channel and a write channel. The read channel is operative to extract, from the disk platter 116, a clock signal, equalize an input read head signal (i.e., read pulse), make a determination regarding a digital state (e.g., logic “1” or “0”) of the input read head signal, and decode read data 122 as a function of the input read head signal. The write channel is operative to encode write data 124 for storage on the disk platter 116 in the form of magnetic field orientations indicative of a logical state of the write data. The read/write channel 102 is assisted by the preamplifier 104, which is configured to drive the write head portion of the read/write head 120 during a write process and to amplify the input signal obtained from the read head portion of the read/write head during a read process.

The interface controller 106 is adapted to control a data interface between the read/write channel 102 and a central processing unit (CPU) or alternative controller, which may include handling interrupts and data transfer protocols common to magnetic drives, optical drives, solid-state drives (SSDs), etc. The interface controller 106 may optionally include an auxiliary buffer, which can be implemented, for example, using random access memory (RAM), for caching and queuing data, providing long data-bursts to improve speed and reduce bus latency. The hard disk controller 110 calculates actuator trajectories and controls the spindle motor 114 and VCM 118, via the motor controller 112, to correctly position and maintain the read/write head 120 on a prescribed track of the disk platter 116.

As previously stated, one disadvantage with bit patterned media recording (BPMR) and heat-assisted magnetic recording (HAMR) is that these approaches, while providing improved recording density, require substantial modifications to the media and heads which significantly increases overall cost. ARMR is seen as an intermediate approach between current perpendicular magnetic recording (PMR) and two-dimensional magnetic recording (TDMR) which provides a significant increase in storage density compared to PMR while avoiding the challenges posed by BPMR and HAMR. Multiple-input single-output (MISO) ARMR uses standard media and an array of read heads, also referred to herein as an array reader, in conjunction with modest changes in read-back signal processing to achieve improved signal-to-noise ratio (SNR) of a single target track that is being read. Similarly, multiple-input multiple-output (MIMO) ARMR uses an array reader configured to retrieve information from multiple tracks for achieving higher data throughput.

TDMR is a known recording architecture intended to support storage densities beyond those of conventional recording systems. TDMR utilizes multiple readers to read from multiple adjacent tracks and uses inter-track interference (ITI) to decode the signal from a target track. The gains achieved from TDMR come primarily from more powerful coding and signal processing algorithms which allow data bits to be stored more densely on a magnetic storage medium (e.g., disk). In a traditional disk architecture with a single read head, reading a single sector with TDMR generally involves reading the sectors on adjacent tracks, requiring additional disk rotations. To circumvent this problem, TDMR disks may use multiple read heads, also referred to as readers, on the same support arm, typically referred to as a slider, thus restoring traditional read service times. One disadvantage of using a multi-reader approach is that there is an inherent offset (i.e., delay) between respective signals obtained from the read heads due, at least in part, to the physical distance separating the read heads. Although manufacturers may provide information regarding the physical distances between the multiple read heads, actual offset between the respective signals obtained from the read heads, referred to herein as reader offset, can vary based on several factors. Such factors which may affect reader offset include, but are not limited to, environmental factors, such as, for example, temperature and mechanical vibration, as well as manufacturing factors, such as, for example, skew between the slider and the disk surface, and alignment of the read heads relative to one another and/or to the slider, among other factors.

ARMR achieves an areal density gain by employing multi-dimensional joint signal processing of multiple read-back signals from the array reader. With reference now to FIG. 2, a block diagram depicts at least a portion of read-back signal processing blocks for an exemplary two-reader ARMR system 200. The system 200 includes two readers 202 positioned to read data on corresponding tracks, or portions of a track, of a magnetic recording medium; particularly, a primary track 204 and an adjacent track 206 proximate to the primary track. The respective read signals obtained from the readers 202 are supplied to corresponding primary preamplifier (PA) 208 and secondary preamplifier 210. Amplified read signals generated by the preamplifiers 208, 210 are supplied to a read channel module 212 for further processing. Specifically, a primary analog front end (AFE) 214 is adapted to receive the amplified read signal generated by the primary preamplifier 208, and a secondary AFE 216 is adapted to receive the amplified read signal generated by the secondary preamplifier 210. The AFEs 214, 216 are operative to convert the analog amplified read signals generated by the preamplifiers 208, 210 to corresponding digital read signals. The digital read signals are supplied to a two-dimensional joint equalizer 218 which is operative to equalize its combined output to an ideal target signal, where the target can be a partial response (PR) target, to thereby generate an equalized signal. The equalized signal generated by the two-dimensional joint equalizer 218 is supplied to a Viterbi-like data detector 220, which is operative to detect the written data stored on the magnetic storage medium from the equalized signal, to thereby generate an output signal of the two-reader system 200. It is to be understood that the output of the data detector 220 can be a hard decision (e.g., “0” or “1”) or a soft decision (e.g., probability of a “0” and/or a “1”) regarding information read from the selected track(s).

The locations of the readers in an ARMR system are characterized by their cross-track separation (CTS) and/or down-track separation (DTS) between readers. Embodiments of the invention are shown and described herein in the context of a multi-reader head including two read-elements (i.e., readers) that are positioned according to a prescribed CTS and DTS. Due to skew, among other factors (e.g., temperature, vibration, etc.), the effective CTS between readers will vary. Further, the larger the DTS between read-elements without skew, denoted by DTS₀ or d, the more the CTS will vary with skew. Likewise, the smaller the DTS between readers in a multi-reader head, the smaller the sensitivity to skew angle. The term “skew angle” as used herein is intended to refer broadly to an angle between a reader assembly, to which one or more readers are attached, and a tangent to a target track to be read. It is to be appreciated that while exemplary embodiments of the invention are described herein in the context of a multi-reader head including two readers, embodiments of the invention are not limited to any specific number of readers.

FIGS. 3A-3C are top plan views conceptually depicting how reader CTS varies with skew angle 302 for an exemplary multi-reader head. In FIG. 3A, a multi-reader head is shown disposed at two different skew angles; namely, 0 and θ degrees. The zero-skew case is indicative of the DTS between the readers being aligned with a tangent to a centerline of a corresponding track being read. It follows that the difference between the two different skew angles is θ 302. The multi-reader head includes two readers, 304 and 306, shown disposed relative to one another for each of the two skew angle scenarios. A certain CTS 308 occurs between the two readers given the skew angle θ and is represented by ζ(θ), also denoted by CTS(θ). Note, that DTS 312 decreases with increasing skew angle θ. It should also be understood that, in one or more embodiments, CTS and DTS are measured in terms of TP 310 (three tracks, e.g., 314, are shown in FIG. 3A). For example, DTS=2 TP means that the down-track separation of two readers of the multi-reader head is equal to two times the track pitch, irrespective of skew angle.

FIG. 3B illustrates the CTS and DTS between two readers at 0 degree skew angle, denoted by CTS₀ and DTS₀, respectively, with v denoting an angle of separation between the readers at zero skew relative to a tangent to a centerline of the corresponding track being read. It should be understood that a multi-reader head having a shorter DTS experiences smaller CTS variations for the same skew angle (e.g., CTS variation is smaller for a multi-reader head having DTS=3 TP compared to that of a multi-reader head having DTS=9 TP). By way of example only and without limitation, for comparison purposes, the bit length (BL) for data being stored on a track is typically a portion of the track pitch (e.g., BL about 0.25 TP; bit aspect ratio (BAR)=4), and a given reader width (RW) is generally larger than the BL (e.g., RW is about 0.6 TP). Here, BAR is defined as the ratio of track pitch to bit length and is unitless (i.e., BAR=TP/BL).

With reference to FIG. 3C, a relationship describing the variation of CTS with skew angle for a given DTS₀ and CTS₀, in accordance with an illustrative embodiment, is written as:

$\begin{matrix} {{{CTS}(\theta)} = \frac{{DTS}_{0} \cdot {\sin\left( {\theta + v} \right)}}{\cos\mspace{14mu} v}} \\ {= \frac{{DTS}_{0} \cdot \left( {{{\sin(\theta)}{\cos(v)}} + {{\cos(\theta)}{\sin(v)}}} \right)}{\cos\mspace{14mu} v}} \end{matrix}$ CTS(θ)=DTS₀ sin(θ)+CTS₀ cos(θ)˜CTS₀+DTS₀θ, for small θ.

Here, a small skew angle θ can be between, for example, about −16 degrees and 16 degrees. In another embodiment, the range of 8 is between about −16 degrees and 20 degrees. Different hardware (e.g., disk platters and read-elements) can have different skew angle ranges defining different zones of operation. It is to be understood, however, that embodiments of the invention are not limited to any specific skew angle or range of angles.

The performance of a system utilizing ARMR will be dependent upon the respective locations of the readers relative to a center of a corresponding target track to be read. By way of illustration only and without limitation, FIG. 4 is a top plan view depicting a two-reader head in various CTS, DTS and skew angle configurations relative to corresponding tracks in an ARMR system. In a first configuration 402, a read head includes a first reader 404 and a second reader 406 having a CTS of 0.9 TP and a DTS of 2 TP at zero skew (i.e., CTS₀=0.9 TP; DTS₀=2 TP). A skew angle of the read head in configuration 402 is −16 degrees, and a CTS between the first and second readers 404, 406 is 0.3 TP (i.e., CTS(−16°)=0.3 TP). With the location of the first reader 404 positioned approximately over a centerline of corresponding track 2, as shown in configuration 402, which may be considered an outer diameter (OD) zone of the magnetic disk/medium, the second reader 406 will be positioned just off the centerline of track 2. Accordingly, this configuration is only suitable for operation in an ARMR MISO mode.

In configuration 408, which may be considered a mid-diameter (MD) zone of the magnetic disk/medium, the skew angle is zero, and therefore a CTS will be CTS₀=0.9 TP and a DTS will be DTS₀=2 TP. In this configuration, the first reader 404 will be positioned over a centerline of corresponding track 2 and the second reader 406 will be positioned over a centerline of corresponding track 3. Consequently, configuration 408 is suitable for use in a MIMO mode of operation. In configuration 410, which may be considered an inner diameter (ID) zone of the magnetic disk/medium, the skew angle is 16 degrees, and therefore the CTS will be 1.4 TP (i.e., CTS(16°)=1.4 TP). In this configuration, with the first reader 404 positioned over a centerline of corresponding track 2, the second reader 406 will be positioned over a boundary between tracks 3 and 4, and therefore configuration 410 would not be well-suited for operation in a MIMO mode. Thus, the exemplary two-reader arrangement with DTS₀=2 TP cannot support a MIMO mode of operation for all skew angles. Rather, as depicted by plot 422 in graph 420, the two-reader arrangement having a DTS of 2 TP and a CTS of 0.9 TP at zero skew can only support MIMO operation for skew angles in a range from about −6 degrees to 8 degrees.

As the DTS between readers increases, the usable range of skew angles in which the two-reader arrangement can be used for MIMO operation becomes increasingly narrower. For example, in configuration 412, the first reader 404 and second reader 406 have a CTS of 0.9 TP and a DTS of 4 TP at zero skew (i.e., CTS₀=0.9 TP; DTS₀=4 TP). A skew angle of the read head in configuration 412 is −8 degrees, and a CTS between the first and second readers 404, 406 is 0.3 TP. With the location of the first reader 404 positioned to the left of the centerline of track 2, the second reader 406 will be positioned to the right of the centerline of track 2. Accordingly, this configuration does not support an ARMR MIMO mode, and instead it is suitable for an ARMR MISO mode for recovering track 2. In configuration 414, with zero skew, the CTS will be 0.9 TP and the DTS will be 4 TP. In this configuration, the first reader 404 will be positioned over a centerline of track 2 and the second reader 406 will be positioned over a centerline of track 3. In this manner, configuration 414 supports a MIMO mode of operation. In configuration 416, the skew angle is 8 degrees and the CTS is 1.4 TP. In this configuration, with the first reader 404 positioned over the centerline of track 2, the second reader 406 will be positioned over a boundary between tracks 3 and 4, and therefore configuration 416, like configuration 412, cannot support a MIMO mode. As depicted by plot 424 in graph 420, the two-reader arrangement having a DTS of 4 TP and a CTS of 0.9 TP at zero skew will only support MIMO operation for skew angles in a range from about −3 degrees to 4 degrees.

As illustrated in FIG. 4, ARMR using two readers suffers large skew-dependent CTS variations, which is undesirable particularly in an ARMR MIMO application. In accordance with embodiments of the invention, by increasing the number of readers employed and selecting a subset of the readers which offer more optimal read performance as a function of the skew, a multi-reader ARMR system having greater skew tolerance is achieved. By selecting outputs from only a subset of the readers, embodiments of the invention are able to capitalize on an increased number of readers without having to significantly increase the number of components and computational overhead in the read channel. Embodiments of the invention are shown and described herein in the context of an array reader comprising three readers which are positioned in various illustrative cross-track spacing and down-track distance configurations, as will be described in further detail in conjunction with FIGS. 5 through 11. While embodiments of the invention are described herein which utilize three readers, of which a subset of two of the three readers is selected for actual processing, it is to be understood that embodiments of the invention are not limited to any specific number of readers.

FIG. 5 is a top plan view depicting exemplary configurations of a read head comprising three readers in a zero-skew position relative to a corresponding magnetic storage medium, according to one or more embodiments of the invention. With reference to FIG. 5, by way of example only and without limitation, in a first configuration 502, a first reader 504, a second reader 506 and a third reader 508 are arranged such that at zero skew, a CTS between the first and second readers (CTS₀ ^(1,2)) is 0.4 TP, a DTS between the first and second readers (DTS₀ ^(1,2)) is 2 TP, a CTS between the first and third readers (CTS₀ ^(1,3)) is 0.0 TP (i.e., the first and third readers are aligned with one another in a direction parallel with a reference line 509 tangent to a corresponding track, Track 2), a DTS between the first and third readers (DTS₀ ^(1,3)) is 4 TP, a CTS between the second and third readers (CTS₀ ^(2,3)) is −0.4 TP, and a DTS between the second and third readers (DTS₀ ^(2,3)) is 2 TP. In configuration 502, the second reader 506 is placed between the first reader 504 and third reader 508 in a down-track direction, and is placed away from the first and third readers in a cross-track direction, on an opposite side of reference line 509. Although embodiments of the invention are not limited to any specific position(s) of the readers, this arrangement of configuration 502 offers a sufficient selection of reader combinations, since CTS between the first and second readers is affected in an opposite manner compared to the CTS between the second and third readers.

In a second configuration 510, the first reader 504, second reader 506 and third reader 508 are arranged such that at zero skew, a CTS between the first and second readers (CTS₀ ^(1,2)) is 0.8 TP, a DTS between the first and second readers (DTS₀ ^(1,2)) is 1 TP, a CTS between the first and third readers (CTS₀ ^(1,3)) is 0.4 TP, a DTS between the first and third readers (DTS₀ ^(1,3)) is 3 TP, a CTS between the second and third readers (CTS₀ ^(2,3)) is −0.4 TP, and a DTS between the second and third readers (DTS₀ ^(2,3)) is 2 TP. The first reader 504 is positioned over Track 1 and the second and third readers 506, 508 are each positioned proximate opposite outside peripheral ends of Track 2, thus enabling the multi-reader head to support MIMO operation. In configuration 510, as in configuration 502, the second reader 506 is placed between the first reader 504 and third reader 508 in a down-track direction, and is placed away from the first and third readers in a cross-track direction, on an opposite side of reference line 509 which bisects the multi-reader head. Again, embodiments of the invention are not limited to any specific position(s) of the readers.

FIG. 6 conceptually depicts an illustrative methodology for selecting a combination of readers as a function of skew angle given a first exemplary placement of readers in a multi-reader head, according to an embodiment of the invention. With reference to FIG. 6, a multi-reader head comprising a first reader 604, a second reader 606 and a third reader 608 is shown in three different skew angle (zone) configurations, 602, 612 and 614. At zero skew (i.e., θ=0°), the CTS between the first and second readers (CTS₀ ^(1,2)) is 0.4 TP, the DTS between the first and second readers (DTS₀ ^(1,2)) is 2 TP, the CTS between the first and third readers (CTS₀ ^(1,3)) is 0 TP (i.e., the first and third readers are aligned with one another in a cross-track dimension), the DTS between the first and third readers (DTS₀ ^(1,3)) is 4 TP, the CTS between the second and third readers (CTS₀ ^(2,3)) is −0.4 TP, and the DTS between the second and third readers (DTS₀ ^(2,3)) is 2 TP.

In a first exemplary zone configuration 602, the skew angle is −16 degrees, making the CTS between the first and second readers (CTS^(1,2)(−16°)) equal to about −0.2 TP, the CTS between the first and third readers (CTS^(1,3)(−16°)) equal to about −1.1 TP, and a CTS between the second and third readers (CTS^(2,3)(−16°)) equal to about −0.93 TP. In this configuration, the first and second readers 604, 606 are positioned over a centerline 610 of track 2 and the third reader 608 is positioned approximately over a center of track 1. In a second exemplary zone configuration 612, the skew angle is 0 degrees, making the CTS between the first and second readers (CTS^(1,2)(0°)) equal to about 0.4 TP, the CTS between the first and third readers (CTS^(1,3)(0°)) equal to 0 TP, and a CTS between the second and third readers (CTS^(2,3)(0°)) equal to −0.4 TP. In this configuration, the first and third readers 604, 608 are positioned over the centerline 610 of track 2 and second reader 606 is positioned over a boundary between tracks 2 and 3. In a third exemplary zone configuration 614, the skew angle is 16 degrees, making the CTS between the first and second readers (CTS^(1,2)(16°)) equal to about 0.9 TP, the CTS between the first and third readers (CTS^(1,3)(16°)) equal to about 1.1 TP, and a CTS between the second and third readers (CTS^(2,3)(16°)) equal to about 0.15 TP. In this configuration, the first reader 604 is positioned over a center of track 1 and the second and third readers 606, 608 are positioned over the centerline 610 of track 2. Plots 620, 622 and 624 in graph 618 of FIG. 6 show exemplary CTS variations between combinations of the first reader (r1) and second reader (r2), r1+r2, the first reader (r1) and third reader (r3), r1+r3, and the second reader (r2) and third reader (r3), r2+r3, respectively, as a function of skew angle θ.

For an exemplary ARMR MISO embodiment, assume that a target CTS range 626 from −0.3 TP to 0.3 TP is desired between any combination of two readers over a skew angle range of ±16 degrees (i.e., |CTS^(i,j)(θ)|<0.3 TP for |θ|<16°, where i and j are integers indicative of reader numbers—first, second or third readers). For skew angles between −16 degrees and about −4 degrees, a combination including the first and second readers 604, 606 is selected, since the CTS between the first and second readers falls within the desired target range 626 (see plot 620); similarly, the CTS between the first and third readers or between the second and third readers falls outside the target range 626 for skew angles between −16 and −4 degrees. For skew angles between about −4 degrees and about 4 degrees, a combination including the first and third readers 604, 608 is selected, since the CTS between the first and third readers falls within the desired target range 626 (see plot 622); similarly, the CTS between the first and second readers or between the second and third readers falls outside the target range 626 for skew angles between −4 and 4 degrees. For skew angles between about 4 degrees and 16 degrees, a combination including the second and third readers 606, 608 is selected, since the CTS between the second and third readers falls within the desired target range 626 (see plot 624); similarly, the CTS between the first and second readers or between the first and third readers falls outside the target range 626 for skew angles between 4 and 16 degrees.

FIG. 7 conceptually depicts an illustrative methodology for selecting a combination of readers as a function of skew angle given a second exemplary placement of readers in a multi-reader head, according to an embodiment of the invention. With reference to FIG. 7, a multi-reader head comprising a first reader 704, a second reader 706 and a third reader 708 is shown in three different skew angle (zone) configurations, 702, 712 and 714. At zero skew (i.e., θ=0°), the CTS between the first and second readers (CTS₀ ^(1,2)) is 0.5 TP, the DTS between the first and second readers (DTS₀ ^(1,2)) is 1.5 TP, the CTS between the first and third readers (CTS₀ ^(1,3)) is 0.1 TP, the DTS between the first and third readers (DTS₀ ^(1,3)) is 4 TP, the CTS between the second and third readers (CTS₀ ^(2,3)) is −0.4 TP, and the DTS between the second and third readers (DTS₀ ^(2,3)) is 2.5 TP.

In a first exemplary zone configuration 702, the skew angle is −16 degrees, making the CTS between the first and second readers (CTS^(1,2)(−16°)) equal to about 0.08 TP, the CTS between the first and third readers (CTS^(1,3)(−16°)) equal to about −1.0 TP, and a CTS between the second and third readers (CTS^(2,3)(−16°)) equal to about −1.1 TP. In this configuration, the first and second readers 704, 706 are positioned on either side of and closely proximate to a centerline 710 of track 2 and the third reader 708 is positioned over a center of track 1. In a second exemplary zone configuration 712, the skew angle is 0 degrees, making the CTS between the first and second readers (CTS^(1,2)(0°)) equal to 0.5 TP, the CTS between the first and third readers)) (CTS^(1,3)(0°)) equal to 0.1 TP, and a CTS between the second and third readers (CTS^(2,3)(0° equal to −0.4 TP. In this configuration, the first and third readers 704, 708 are positioned on either side of and closely proximate to the centerline 710 of track 2 and the second reader 706 is positioned over a boundary between tracks 2 and 3. In a third exemplary zone configuration 714, the skew angle is 16 degrees, making the CTS between the first and second readers (CTS^(1,2)(16°)) equal to about 0.9 TP, the CTS between the first and third readers (CTS^(1,3)(16°)) equal to about 1.2 TP, and a CTS between the second and third readers (CTS^(2,3)(16°)) equal to 0.3 TP. In this configuration, the first reader 704 is positioned over a center of track 1 and the second and third readers 706, 708 are positioned on either side of and closely proximate to the centerline 710 of track 2. Plots 720, 722 and 724 in graph 718 of FIG. 7 show exemplary CTS variations between combinations of the first and second readers (r1+r2), the first and third readers (r1+r3), and the second and third readers (r2+r3), respectively, as a function of skew angle θ.

For an exemplary ARMR MISO embodiment, assume that a target CTS range 726 from −0.3 TP to 0.3 TP is desired between any combination of two readers over a skew angle range of ±16 degrees (i.e., |CTS^(i,j)(θ)|<0.3 TP for |θ|<16°, where i and j are integers). For skew angles between −16 degrees and about −6 degrees, a combination including the first and second readers 704, 706 is selected, since the CTS between the first and second readers falls within the desired target range 726 (see plot 720); similarly, the CTS between the first and third readers or between the second and third readers falls outside the target range 726 for skew angles between −16 and about −6 degrees. For skew angles between about −6 degrees and about 3 degrees, a combination including the first and third readers 704, 708 is selected, since the CTS between the first and third readers falls within the desired target range 726 (see plot 722); similarly, the CTS between the first and second readers or between the second and third readers falls outside the target range 726 for skew angles between −6 and 3 degrees. For skew angles between about 3 degrees and 16 degrees, a combination including the second and third readers 706, 708 is selected, since the CTS between the second and third readers falls within the desired target range 726 (see plot 724); similarly, the CTS between the first and second readers or between the first and third readers falls outside the target range 726 for skew angles between about 3 and 16 degrees.

FIG. 8 conceptually depicts an illustrative methodology for selecting a combination of readers as a function of skew angle given a third exemplary placement of readers in a multi-reader head, according to an embodiment of the invention. With reference to FIG. 8, a multi-reader head comprising a first reader 804, a second reader 806 and a third reader 808 is shown in three different skew angle (zone) configurations, 802, 812 and 814. At zero skew (i.e., θ=0°), the CTS between the first and second readers (CTS₀ ^(1,2)) is 0.6 TP, the DTS between the first and second readers (DTS₀ ^(1,2)) is 0.25 TP, the CTS between the first and third readers (CTS₀ ^(1,3)) is 0.3 TP, the DTS between the first and third readers (DTS₀ ^(1,3)) is 2.25 TP, the CTS between the second and third readers (CTS₀ ^(2,3)) is −0.3 TP, and the DTS between the second and third readers (DTS₀ ^(2,3)) is 2 TP.

In a first exemplary zone configuration 802, the skew angle is −16 degrees. At a skew angle of 16 degrees, the CTS between the first and second readers (CTS^(1,2)(−16°)) is equal to about 0.5 TP, the CTS between the first and third readers (CTS^(1,3)(−16°)) is equal to −0.3 TP, and a CTS between the second and third readers (CTS^(2,3)(−16°)) is equal to about −0.8 TP. In this configuration, the first and third readers 804, 808 are positioned over a centerline 810 of track 2 and the second reader 806 is positioned over a center of track 3. In a second exemplary zone configuration 812, the skew angle is 0 degrees, making the CTS between the first and second readers (CTS^(1,2)(0°)) equal to 0.6 TP, the CTS between the first and third readers (CTS^(1,3)(0°)) equal to 0.3 TP, and a CTS between the second and third readers (CTS^(2,3)(0°)) equal to −0.3 TP. In this configuration, the first reader 804 is positioned over a center of track 1 and the second and third readers 806, 808 are positioned on opposite sides of the centerline 810 of track 2, but still within the boundaries of track 2. In a third exemplary zone configuration 814, the skew angle is 16 degrees, making the CTS between the first and second readers (CTS^(1,2)(16°)) equal to about 0.65 TP, the CTS between the first and third readers (CTS^(1,3)(16°)) equal to about 0.9 TP, and a CTS between the second and third readers (CTS^(2,3)(16°)) equal to about 0.28 TP. In this configuration, the first reader 804 is positioned over track 1 and the second and third readers 806, 808 are positioned over the centerline 810 of track 2. Plots 820, 822 and 824 in graph 818 of FIG. 8 show exemplary CTS variations between combinations of the first and second readers (r1+r2), the first and third readers (r1+r3), and the second and third readers (r2+r3), respectively, as a function of skew angle θ.

For an exemplary ARMR MISO embodiment, assume that a target CTS range 826 from −0.3 TP to 0.3 TP is desired between any combination of two readers over a skew angle range of ±16 degrees (i.e., |CTS^(i,j)(θ)|<0.3 TP for |θ|<16°, where i and j are integers). With reference to graph 818, for the illustrative placement of readers shown in FIG. 8, it is evident that a selected combination of readers which includes the first and second readers 804, 806 does not yield a CTS that falls within the prescribed range 826 for any skew angles in the range of ±16 degrees (see plot 820). Rather, only selected combinations including the first and third readers 804, 808 and the second and third readers 806, 808 provide a CTS which falls within the prescribed range 826, depending on the skew angle. More particularly, for skew angles between −16 degrees and zero degrees, a combination including the first and third readers 804, 808 is selected, since the CTS between the first and third readers is within the desired target CTS range 826 (see plot 822). For skew angles between zero degrees and 16 degrees, a combination including the second and third readers 806, 808 is selected, since the CTS between the second and third readers is within the desired target range 826 (see plot 824).

While the various illustrative reader placement scenarios shown in FIGS. 5-8 are suitable for use in a MISO ARMR application, it is to be understood that aspects according to embodiments of the invention are easily extended to support MIMO ARMR operation. By way of example only and without limitation, FIGS. 9-11 conceptually depict different reader placement arrangements suitable for use in a MIMO ARMR application, as will be described in further detail below.

Specifically, FIG. 9 conceptually depicts an illustrative methodology for selecting a combination of readers as a function of skew angle given a first exemplary placement of readers in a multi-reader head configured for MIMO operation, according to an embodiment of the invention. With reference to FIG. 9, a multi-reader head comprising a first reader 904, a second reader 906 and a third reader 908 is shown in three different skew angle (zone) configurations, 902, 912 and 914. At zero skew (i.e., θ=0°), the CTS between the first and second readers (CTS₀ ^(1,2)) is 0.7 TP, the DTS between the first and second readers (DTS₀ ^(1,2)) is 2 TP, the CTS between the first and third readers (CTS₀ ^(1,3)) is 0 TP, the DTS between the first and third readers (DTS₀ ^(1,3)) is 4 TP, the CTS between the second and third readers (CTS₀ ^(2,3)) is −0.7 TP, and the DTS between the second and third readers (DTS₀ ^(2,3)) is 2 TP.

In a first exemplary zone configuration 902, the skew angle is −16 degrees. At a skew of 16 degrees, the CTS between the first and second readers (CTS^(1,2)(−16°)) is about 0.1 TP, the CTS between the first and third readers (CTS^(1,3)(−16°)) is −1.1 TP, and a CTS between the second and third readers (CTS^(2,3)(−16°)) is about −1.2 TP. In this configuration, the first and second readers 904, 906 are positioned about over a centerline 911 of track 3 and the third reader 908 is positioned over a centerline 910 of track 2. In a second exemplary zone configuration 912, the skew angle is 0 degrees, resulting in a CTS between the first and second readers (CTS^(1,2)(0° equal to 0.7 TP, the CTS between the first and third readers (CTS^(1,3)(0°)) equal to 0 TP, and the CTS between the second and third readers (CTS^(2,3)(0°)) equal to −0.7 TP. In this configuration, the first and third readers 904, 908 are positioned over track 2, just off the centerline 910 of track 2, and the second reader 906 is positioned over track 3, just off the centerline 911 of track 3. In a third exemplary zone configuration 914, the skew angle is 16 degrees, making the CTS between the first and second readers (CTS^(1,2)(16°)) equal to about 1.2 TP, the CTS between the first and third readers (CTS^(1,3)(16°)) equal to 1.1 TP, and the CTS between the second and third readers (CTS^(2,3)(16°)) equal to about −0.1 TP. In this configuration, the first reader 904 is positioned over the centerline 910 of track 2, and the second and third readers 906, 908 are positioned over track 3, with the third reader over the centerline 911 of track 3 and the second reader just off the centerline of track 3. Plots 920, 922 and 924 in graph 918 of FIG. 9 show exemplary CTS variations between combinations of the first and second readers (r1+r2), the first and third readers (r1+r3), and the second and third readers (r2+r3), respectively, as a function of skew angle θ.

In order to detect two tracks in a MIMO application, the CTS between readers is larger compared to a MISO application. Thus, for the exemplary ARMR MIMO embodiment, assume there are two desired target CTS ranges between any combination of two readers over a skew angle range of ±16 degrees; namely, a first range 926 corresponding to a CTS from 0.7 TP to 1.1 TP, and a second range 928 corresponding to CTS from −0.7 TP to −1.1 TP, as shown in graph 918 (i.e., 0.7 TP<|CTS^(i,j)(θ)|<1.1 TP for |θ|<16°, where i and j are integers indicative of reader numbers). It is to be appreciated that embodiments of the invention are not limited to any specific CTS range or ranges.

With reference to graph 918, for the illustrative placement of readers shown in FIG. 9, it is evident that for skew angles between −16 degrees and about −11 degrees, a combination including the first and third readers 9θ4, 908 is selected (see plot 922), and for skew angles between about −11 degrees and 0 degrees, a combination including the second and third readers 906, 908 is selected (see plot 924), since these selected reader combinations exhibit cross-track separations that are within the second target range 928. Similarly, for skew angles between 0 degrees and about 11 degrees, a combination including the first and second readers 904, 906 is selected (see plot 920), and for skew angles between about 11 degrees and 16 degrees, a combination including the first and third readers 904, 908 is again selected (see plot 922), since these selected reader combinations exhibit cross-track separations that are within the first target range 926.

FIG. 10 conceptually depicts an illustrative methodology for selecting a combination of readers as a function of skew angle given a second exemplary placement of readers in a multi-reader head configured for MIMO operation, according to an embodiment of the invention. As shown in FIG. 10, a multi-reader head comprising a first reader 1004, a second reader 1006 and a third reader 1008 is shown in three different skew angle (zone) configurations, 1002, 1012 and 1014. The multi-reader head is characterized at zero skew as having a CTS between the first and second readers (CTS₀ ^(1,2)) of 0.8 TP, a DTS between the first and second readers (DTS₀ ^(1,2)) of 1 TP, a CTS between the first and third readers (CTS₀ ^(1,3)) of 0.2 TP, a DTS between the first and third readers (DTS₀ ^(1,3)) of 3 TP, a CTS between the second and third readers (CTS₀ ^(2,3)) of −0.6 TP, and a DTS between the second and third readers (DTS₀ ^(2,3)) of 2 TP.

In a first exemplary zone configuration 1002, at a skew angle of −16 degrees, the CTS between the first and second readers (CTS^(1,2)(−16°)) is about 0.5 TP, the CTS between the first and third readers (CTS^(1,3)(−16°)) is about −0.65 TP, and a CTS between the second and third readers (CTS^(2,3)(−16°)) is about −1.1 TP. In this configuration, the first and third readers 1004, 1008 are positioned over track 2, on opposite sides of a centerline 1010 of track 2 but within the boundaries of track 2, and the second reader 1006 is positioned about over a centerline 1011 of track 3. In a second exemplary zone configuration 1012, the skew angle is 0 degrees, and therefore the CTS between the first and second readers (CTS^(1,2)(0°)) is 0.8 TP, the CTS between the first and third readers (CTS^(1,3)(0°)) is 0.2 TP, and the CTS between second and third readers (CTS^(2,3)(0°)) is −0.6 TP, as previously stated. In this configuration, the first and third readers 1004, 1008 are positioned over track 2, with the first reader over the centerline 1010 of track 2 and the third reader positioned just off the centerline of track 2, and the second reader 1006 is positioned over the centerline 1011 of track 3. In a third exemplary zone configuration 1014, the skew angle is 16 degrees, resulting in a CTS between the first and second readers (CTS^(1,2)(16°)) of about 1.05 TP, a CTS between the first and third readers (CTS^(1,3)(16°)) of about 1.05 TP, and a CTS between the second and third readers (CTS^(2,3)(16°)) of about 0 TP. In this configuration, the first reader 1004 is positioned over the centerline 1010 of track 2 and the second and third readers 1006, 1008 are positioned over track 3, with the third reader positioned over the centerline 1011 of track 3 and the second reader positioned just off the centerline of track 3. Plots 1020, 1022 and 1024 in graph 1018 of FIG. 10 show exemplary CTS variations between combinations of the first and second readers (r1+r2), the first and third readers (r1+r3), and the second and third readers (r2+r3), respectively, as a function of skew angle θ.

For the illustrative ARMR MIMO embodiment shown in FIG. 10, there are two desired target CTS ranges between any combination of two readers over a skew angle range of ±16 degrees; namely, a first range 1026 corresponding to a CTS from 0.7 TP to 1.1 TP, and a second range 1028 corresponding to CTS from −0.7 TP to −1.1 TP, as shown in graph 1018 (i.e., 0.7 TP<|CTS^(i,j)(θ)|<1.1 TP for |θ|<16°, where i and j are integers indicative of reader numbers). With reference to graph 1018, for the illustrative placement of readers shown in FIG. 10, it is evident that for skew angles between −16 degrees and about −5 degrees, a combination including the second and third readers 1006, 1008 is selected (see plot 1024), since this selected reader combination exhibits a CTS that is within the second target range 1028. For skew angles between about −5 degrees and about 12 degrees, a combination including the first and second readers 1004, 1006 is selected (see plot 1020), and for skew angles between about 12 degrees and 16 degrees, a combination including the first and third readers 1004, 1008 is selected (see plot 1022), since these selected reader combinations exhibit cross-track separations that are within the first target range 1026.

FIG. 11 conceptually depicts an illustrative methodology for selecting a combination of readers as a function of skew angle given a third exemplary placement of readers in a multi-reader head configured for MIMO operation, according to an embodiment of the invention. As shown in FIG. 11, a multi-reader head comprising a first reader 1104, a second reader 1106 and a third reader 1108 is shown in three different skew angle (zone) configurations, 1102, 1112 and 1114. The multi-reader head is characterized at zero skew as having a CTS between the first and second readers (CTS₀ ^(1,2)) of 0.95 TP, a DTS between the first and second readers (DTS₀ ^(1,2)) of 0.25 TP, a CTS between the first and third readers (CTS₀ ^(1,3)) of 0.45 TP, a DTS between the first and third readers (DTS₀ ^(1,3)) of 2.25 TP, a CTS between the second and third readers (CTS₀ ^(2,3)) of −0.5 TP, and a DTS between the second and third readers (DTS₀ ^(2,3)) of 2 TP.

In a first exemplary zone configuration 1102, at a skew angle of −16 degrees, the CTS between the first and second readers (CTS^(1,2)(−16°)) is about 0.85 TP, the CTS between the first and third readers (CTS^(1,3)(−16°)) is about −0.2 TP, and a CTS between the second and third readers (CTS^(2,3)(−16°)) is about −1.05 TP. In this configuration, the first and third readers 1104, 1108 are positioned over track 2, on opposite sides of a centerline 1110 of track 2 but within the boundaries of track 2, and the second reader 1106 is positioned about over a centerline 1111 of track 3. In a second exemplary zone configuration 1112, the skew angle is 0 degrees, and therefore the CTS between the first and second readers (CTS^(1,2)(0°)) is 0.95 TP, the CTS between the first and third readers (CTS^(1,3)(0°)) is 0.45 TP, and the CTS between second and third readers (CTS^(2,3)(0°)) is −0.5 TP, as previously stated. In this configuration, the first and third readers 1104, 1108 are positioned over track 2, with the first reader over the centerline 1110 of track 2 and the third reader positioned just off the centerline of track 2, and the second reader 1106 is positioned over the centerline 1111 of track 3. In a third exemplary zone configuration 1114, the skew angle is 16 degrees, resulting in a CTS between the first and second readers (CTS^(1,2)(16°)) of about 1 TP, a CTS between the first and third readers (CTS^(1,3)(16°)) of about 1.1 TP, and a CTS between the second and third readers (CTS^(2,3)(16°)) of about 0.1 TP. In this configuration, the first reader 1104 is positioned over the centerline 1110 of track 2 and the second and third readers 1106, 1108 are positioned over track 3, with the third reader positioned over the centerline 1111 of track 3 and the second reader positioned just off the centerline of track 3. Plots 1120, 1122 and 1124 in graph 1118 of FIG. 11 show exemplary CTS variations between combinations of the first and second readers (r1+r2), the first and third readers (r1+r3), and the second and third readers (r2+r3), respectively, as a function of skew angle θ.

The illustrative ARMR MIMO embodiment shown in FIG. 11 assumes two desired target CTS ranges between any combination of two readers over a skew angle range of ±16 degrees; namely, a first range 1126 corresponding to a CTS from 0.7 TP to 1.1 TP, and a second range 1128 corresponding to CTS from −0.7 TP to −1.1 TP, as shown in graph 1118 (i.e., 0.7 TP<|CTS^(i,j)(θ)|<1.1 TP for |θ|<16°, where i and j are integers indicative of reader numbers). With reference to graph 1118, for the illustrative placement of readers shown in FIG. 11, it is evident that for skew angles between −16 degrees and about −12 degrees, a combination including the second and third readers 1106, 1108 is selected (see plot 1124), since this selected reader combination exhibits a CTS that is within the second target range 1128. Alternatively, a combination which includes the first and second readers 1104, 1106 can also be used, since this selected combination exhibits a CTS that falls within the first target range 1126. For skew angles between about −12 degrees and about 14 degrees, a combination including the first and second readers 1104, 1106 is selected (see plot 1120), and for skew angles between about 14 degrees and 16 degrees, a combination including the first and third readers 1104, 1108 is selected (see plot 1122), since these selected reader combinations exhibit cross-track separations that are within the first target range 1126.

It is to be appreciated that embodiments of the present invention are not limited to any specific thresholds at which a selected combination of readers is switched to a different combination of readers. For example, because there is substantial overlap between the combination which includes the first and second readers and the combination which includes the first and third readers in the first target range 1126, the threshold at which reader combination selection occurs can be changed from 14 degrees to 8 degrees, such that for skew angels in the range of −12 degrees to 8 degrees, the combination including the first and second readers is selected, and for skew angles between 8 degrees and 16 degrees, the combination including the first and third readers is selected.

Regardless of the particular arrangement of readers in the multi-reader head, embodiments of the invention dynamically change which subset of readers is utilized, for supplying read signals to the read channel for further processing, as a function of the skew angle and CTS between readers. In this manner, embodiments of the invention achieve improved read performance compared to alternative approaches which employ a fixed reader configuration.

Although embodiments of the invention are not limited to any specific arrangement of the readers, for a three-reader head, arrangements in which the second reader (i.e., the middle reader, in a down-track direction) is placed on one side of a centerline of the head and the first and third readers are placed on the other side of the centerline (in a cross-track direction) provide favorable performance over a wide range of skew angles. In the general case, a multi-reader head is configured, according to one or more embodiments, such that for at least a subset of the plurality of readers in the multi-reader head, adjacent readers are located on opposite sides (in a cross-track direction) of a centerline of the multi-reader head, the centerline being oriented in a down-track direction (perpendicular to the cross-track direction). According to one or more embodiments, the multi-reader head is configured such that at zero skew, CTS and DTS between readers are appropriate for a desired mode of operation in the ARMR system (e.g., MISO or MIMO operation).

It is to be appreciated that, although described herein in the context of a multi-reader head including three readers, techniques according to embodiments of the invention can be extended to multi-reader heads comprising more than three readers. By way of illustration only and without loss of generality, FIG. 12 is a top plan view depicting exemplary configurations of a read head comprising four readers in a zero-skew position relative to a corresponding magnetic storage medium, according to one or more embodiments of the invention. More particularly, with reference to FIG. 12, a multi-reader head according to an embodiment of the invention comprises four readers, 1204, 1206, 1208 and 1210; two readers (e.g., 1204 and 1208) placed on one side of a centerline 1211 of the head and two readers (e.g., 1206 and 1210) placed on an opposite side of the centerline of the head in a cross-track direction. Although FIG. 12 depicts two different arrangements of the readers, namely, configurations 1202 and 1212, each configuration characterized by prescribed cross-track and down-track distances between the readers, it is to be understood that embodiments of the invention are not limited to any specific arrangement of the readers.

As previously stated, a determination as to which subset of the readers to use in reading data stored on a corresponding track of a magnetic storage medium is based, at least in part, on skew angle, which varies as a function of the particular zone of the medium being read, and the CTS between respective readers. The CTS between readers is often specified by a manufacturer based on prescribed design criteria, although the CTS may vary due to manufacturing tolerances and environmental characteristics (e.g., temperature, vibration, etc.), among other factors. CTS information for the readers may be obtained from manufacturer specifications, according to one or more embodiments. In one or more alternative embodiments, CTS information for the readers is estimated using known CTS estimation techniques. For example, in accordance with one or more embodiments, CTS information for the readers is estimated from read-back signal processing, such as may be performed during a calibration operation.

Once the CTS information for the readers is determined as a function of skew angle for a prescribed range of skew angles (e.g., about ±16 degrees), reader combinations providing more optimal read performance in comparison to other combinations of readers for a given skew angle are pre-computed and stored (e.g., in a zone table or other storage element) for each zone of the medium to be read. Performance may be computed, according to one or more embodiments, as a function of measured amplitudes of the corresponding read signals obtained from each combination of readers, for example. During read-back, the stored reader combination corresponding to a given zone in which the multi-reader head is operating is selected for further processing.

FIG. 13 is a block diagram depicting at least a portion of an exemplary read channel 1300 in which one or more aspects of the invention are employed that is suitable for use in a multi-reader ARMR system, according to an embodiment of the invention. The read channel 1300, in this embodiment, is adapted for use in conjunction with a multi-reader head comprising three readers and operative to process signals from any subset of two readers, although embodiments of the invention are not limited to use with a read channel comprising two read signal paths.

The read channel 1300 includes a controller 1302 configured to receive, as inputs, read signals from three corresponding readers; namely, reader 1, reader 2 and reader 3. It is to be understood that embodiments of the invention are not limited to using three readers, as previously explained. The controller 1302 is configured to select a subset of the available read signals (two, in this example, although embodiments of the invention are not limited to the selection of two read signals) which provides enhanced read performance as outputs supplied to corresponding functional blocks for subsequent processing by the read channel 1300. Once the CTS information for the readers is determined as a function of skew angle for a prescribed range of skew angles (e.g., about ±16 degrees), a zone table 1304 coupled with the controller 1302 is configured to store pre-computed reader combinations providing more optimal read performance in comparison to other combinations of readers for each zone of the medium to be read. Performance may be computed, for example, as a function of measured amplitudes of the corresponding read signals obtained from each combination of readers. During read-back, the stored reader combination corresponding to a given zone is retrieved from the zone table 1304 by the controller 1302, and this retrieved reader combination is then used by the controller in selecting a desired subset of available readers for further processing by the read channel 1300. In accordance with one or more embodiments, the selection of which combination of readers to use, as determined by the controller 1302, is updated (e.g., at prescribed time intervals, on-the-fly, etc.) as the zone (and hence the skew angle) in which the multi-reader head is operating changes. The controller 1302, according to one or more embodiments, is further configured to locate the reader assembly over the target tracks(s) of the medium being read.

The read channel further includes a first analog front end (AFE) 1306 and a first analog-to-digital converter (ADC) 1308 coupled with an output of the first AFE. The first AFE 1306 is adapted to receive one of the read signals supplied by the controller 1302, either in an unamplified form (in which case the first AFE optionally includes a preamplifier or other amplification circuitry) or from a preamplifier (not explicitly shown, but implied) coupled in a signal path between the corresponding reader and the first AFE, and to generate a first analog read signal as an output thereof. The first AFE 1306 may, in one or more embodiments, include signal processing circuitry (e.g., filters, etc.) for reducing noise or otherwise improving a quality of the first analog read signal. The first ADC 1308 is adapted to receive the first analog read signal and to generate, as a function of the first analog read signal, a first digital read signal. The first digital read signal is a digitized (i.e., sampled) version of the first analog read signal, sampled at prescribed discrete time intervals based on a sampling period of the first ADC.

Likewise, the read channel 1300 includes a second AFE 1310 and a second ADC 1312 coupled with an output of the second AFE. The second AFE 1310 is configured to receive another of the read signals supplied by the controller 1302, either in an unamplified form (in which case the second AFE optionally includes a preamplifier or other amplification circuitry) or from a preamplifier (not explicitly shown, but implied) coupled in a signal path between the second reader and the second AFE, and to generate a second analog read signal as an output thereof. The second AFE 1310 may, in one or more embodiments, include signal processing circuitry (e.g., filters, etc.) for reducing noise or otherwise improving a quality of the second analog read signal. The second ADC 1312 is configured to receive the second analog read signal and to generate, as a function of the second analog read signal, a second digital read signal. The second digital read signal is a digitized version of the second analog read signal, sampled at prescribed discrete time intervals based on a sampling period of the second ADC.

In one or more embodiments, the first and second ADCs 1308 and 1312, respectively, are configured to exchange information with one another or otherwise function together jointly, as represented by connection 1313. For example, reader 1 can be configured as a primary reader and reader 2 can be sampled by the phase of reader 1. Alternatively, the outputs of the first and second AFEs 1306 and 1310, respectively, can be sampled jointly; that is, by a joint ADC (not explicitly shown but represented functionally by ADCs 1308 and 1312) configured to receive, as inputs, the respective outputs of the AFEs 1306, 1310 and to generate corresponding ADC outputs.

With continued reference to FIG. 13, the read channel 1300 comprises a joint equalizer module 1314 adapted to receive the first digital read signal generated by the first ADC 1308 and the second digital read signal generated by the second ADC 1312, and is configured to generate an equalized output signal. To make a determination regarding a logical (i.e., digital) state (e.g., logic “1” or “0”) of a target track or tracks, the equalizer output signal is supplied to a detector 1316 which is configured to decode the read data from the equalized output signal as a function of the first and second input read signals and to generate a data output signal, DATA OUT, as a function of the equalized output signal. The determination regarding the logical state of the information read from the target track(s) can be in the form of a hard decision (e.g., a logic “0” or “1”) or a soft decision (e.g., a probability relating to a particular logical state of the information read from the target track).

As will be appreciated by one skilled in the art, embodiments of the present invention may be implemented as an apparatus, system, method or computer program product. Accordingly, aspects of the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to as a “circuit,” “module” or “system.” Furthermore, embodiments of the present invention may take the form of a computer program product embodied in one or more non-transitory machine-readable medium(s) having machine-readable program code embodied thereon.

One or more embodiments of the invention, or elements thereof, can be implemented in the form of an apparatus including a memory and at least one processor coupled with the memory and configured to perform exemplary method steps. In this regard, one or more embodiments of the invention make use of software running on a general purpose computer or workstation which, when configured by the software, becomes a physical special purpose machine operative to perform methods in accordance with embodiments described herein. With reference to FIG. 14, such an implementation might employ, for example, a processor 1402, a memory 1404, and an input/output interface formed, for example, by a display 1406 and a keyboard 1408. The term “processor” as used herein is intended to include any processing device, such as, for example, one that includes a CPU (central processing unit) and/or other forms of processing circuitry. Further, the term “processor” may refer to more than one individual processor. The term “memory” is intended to include memory associated with a processor or CPU, such as, for example, RAM (random access memory), ROM (read only memory), a fixed memory device (for example, hard drive), a removable memory device (for example, diskette), a flash memory and the like. In addition, the phrase “input/output interface” as used herein, is intended to include, for example, one or more mechanisms for inputting data to the processing unit (for example, mouse), and one or more mechanisms for providing results associated with the processing unit (for example, printer). The processor 1402, memory 1404, and input/output interface such as display 1406 and keyboard 1408 can be interconnected, for example, via bus 1410 as part of a data processing unit 1412. Suitable interconnections, for example via bus 1410, can also be provided to a network interface 1414, such as a network card, which can be provided to interface with a computer network, and to a media interface 1416, such as a diskette or CD-ROM drive, which can be provided to interface with media 1418.

Accordingly, computer software including instructions or code for performing methodologies according to embodiments of the invention, as described herein, may be stored in one or more of the associated memory devices (for example, ROM, fixed or removable memory) and, when ready to be utilized, loaded in part or in whole (for example, into RAM) and implemented by a CPU. Such software could include, but is not limited to, firmware, resident software, microcode, and the like.

A data processing system suitable for storing and/or executing program code will include at least one processor 1402 coupled directly or indirectly with memory elements 1404 through a system bus 1410. The memory elements can include local memory employed during actual implementation of the program code, bulk storage, cache memories and embedded memory which provide temporary storage of at least a portion of program code in order to reduce the number of times the code must be retrieved from bulk storage during implementation.

Input/output or I/O devices (including but not limited to keyboards 1408, displays 1406, pointing devices, and the like) can be coupled to the system either directly (such as via bus 1410) or through intervening I/O controllers (omitted for clarity).

Network adapters such as network interface 1414 are also coupled with the system, in one or more embodiments of the invention, to enable the data processing system to become coupled with other data processing systems or remote printers or storage devices through intervening private or public networks. Modems, cable modem and Ethernet cards are just a few of the currently available types of network adapters.

As noted, embodiments of the present invention may take the form of a computer program product embodied in one or more non-transitory machine- or computer-readable medium(s) having computer-readable program code embodied thereon. Any combination of one or more computer-readable medium(s) may be utilized. The computer-readable medium may be a computer-readable signal medium or a computer-readable storage medium. A computer-readable storage medium may be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. Media block 1418 is a non-limiting example. More specific examples (a non-exhaustive list) of the computer-readable storage medium would include the following: an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing. In one or more embodiments, a computer-readable storage medium is any tangible medium that can contain or store, in a non-transitory manner, a program for use by or in connection with an instruction execution system, apparatus, or device.

Computer program code for carrying out operations according to one or more embodiments of the invention are written in any combination of one or more programming languages, including an object-oriented programming language such as Java, Smalltalk, C++ or the like and conventional procedural programming languages, such as the “C” programming language or similar programming languages. The program code may execute entirely on the user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer may be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider).

The computer program code, in one or more embodiments, is loaded onto a computer, other programmable data processing apparatus, or other devices to cause a series of operational steps to be performed on the computer, other programmable apparatus or other devices to produce a computer-implemented process such that the instructions which execute on the computer or other programmable apparatus provide processes for implementing functions/acts specified in the flowchart and/or block diagram block or blocks.

The block diagrams in the figures depict illustrative architectures, functionality, and operation of implementations of systems, methods and computer program products according to embodiments of the present invention. In this regard, each block shown in the block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing specified functions. It should also be noted that, in one or more embodiments, functions represented by the blocks may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be appreciated that each block of the block diagrams, and combinations of blocks in the block diagrams, can be implemented by special purpose hardware-based systems that perform the specified functions or acts, or combinations of special purpose hardware and computer instructions.

It should be understood that any of the methods described herein can include an additional step of providing a system comprising distinct software modules embodied on a non-transitory computer-readable storage medium; the modules include, in one or more embodiments, any or all of the elements depicted in the block diagrams and/or described herein; by way of example only and without limitation, a joint equalization module and a detection module. The method steps can then be carried out using the distinct software modules and/or sub-modules of the system, executing on one or more hardware processors 1402. Further, a computer program product can include a computer-readable storage medium with code adapted to be implemented to carry out one or more method steps described herein, including the provision of the system with the distinct software modules.

In any case, it should be understood that the components illustrated herein may be implemented in various forms of hardware, software, or combinations thereof; for example, application specific integrated circuit(s) (ASICs), functional circuitry, one or more appropriately programmed general purpose digital computers with associated memory, and the like. Given the teachings of the invention provided herein, one of ordinary skill in the related art will be able to contemplate other implementations of the components of the invention.

In an integrated circuit implementation of one or more embodiments of the invention, multiple identical die are typically fabricated in a repeated pattern on a surface of a semiconductor wafer. Each such die may include a device described herein, and may include other structures and/or circuits. The individual dies are cut or diced from the wafer, then packaged as integrated circuits. One skilled in the art would know how to dice wafers and package die to produce integrated circuits. Any of the exemplary circuits illustrated in the accompanying figures, or portions thereof, may be part of an integrated circuit. Integrated circuits so manufactured are considered part of this invention.

Embodiments of the invention are suitable for use in conjunction with a virtual storage system 1500 comprising multiple storage devices 1502-1 through 1502-N, possibly of multiple different types, as illustrated in FIG. 15. For example, the storage devices 1502-1 through 1502-N may be implemented using all hard disk drives (HDDs), all solid-state drives (SSDs), or using a combination of one or more HDDs and one or more SSDs. Other storage device types are similarly contemplated. The virtual storage system 1500, also referred to as a storage virtualization system, illustratively comprises a virtual storage controller 1504 coupled with a redundant array of independent devices (RAID) system 1506. As will be known by those skilled in the art, RAID is a storage technology that provides increased reliability, among other features, through redundancy. This is accomplished by combining multiple physical storage components (e.g., HDDs, SSDs, etc.) into a logical (i.e., virtual) unit, where data is distributed across the multiple storage components in one of a plurality of ways, generally referred to as “RAID levels.” The RAID system 1506 more specifically comprises N distinct storage devices denoted 1502-1, 1502-2, . . . 1502-N, where N is an integer greater than one. As previously stated, all storage devices 1502-1 through 1502-N need not be of the same type. Furthermore, one or more of the storage devices 1502-1 through 1502-N of the RAID system 1506 are assumed to be configured to include apparatus and/or circuitry as disclosed herein. These and other virtual storage systems comprising multiple storage devices (e.g., HDDs, SSDs, or some combination of HDDs and SSDs), are considered embodiments of the invention.

The illustrations of embodiments of the invention described herein are intended to provide a general understanding of the structure of various embodiments, and they are not intended to serve as a complete description of all the elements and features of apparatus and systems that might make use of the structures described herein. Many other embodiments will become apparent to those skilled in the art given the teachings herein; other embodiments are utilized and derived therefrom, such that structural and logical substitutions and changes can be made without departing from the scope of this disclosure. The drawings are also merely representational and are not drawn to scale. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense.

Embodiments of the invention are referred to herein, individually and/or collectively, by the term “embodiment” merely for convenience and without intending to limit the scope of this application to any single embodiment or inventive concept if more than one is, in fact, shown. Thus, although specific embodiments have been illustrated and described herein, it should be understood that an arrangement achieving the same purpose can be substituted for the specific embodiment(s) shown; that is, this disclosure is intended to cover any and all adaptations or variations of various embodiments. Combinations of the above embodiments, and other embodiments not specifically described herein, will become apparent to those of skill in the art given the teachings herein.

The abstract is provided to comply with 37 C.F.R. §1.72(b), which requires an abstract that will allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. In addition, in the foregoing Detailed Description, it can be seen that various features are grouped together in a single embodiment for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments require more features than are expressly recited in each claim. Rather, as the appended claims reflect, inventive subject matter lies in less than all features of a single embodiment. Thus the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as separately claimed subject matter.

Given the teachings of embodiments of the invention provided herein, one of ordinary skill in the art will be able to contemplate other implementations and applications of the techniques of embodiments of the invention. Although illustrative embodiments of the invention have been described herein with reference to the accompanying drawings, it is to be understood that embodiments of the invention are not limited to those precise embodiments, and that various other changes and modifications are made therein by one skilled in the art without departing from the scope of the appended claims. 

What is claimed is:
 1. A method for enhancing read performance in an array-reader based magnetic recording (ARMR) system, the method comprising: obtaining cross-track separation (CTS) information for a plurality of readers in a multi-reader head of the ARMR system, the CTS information defining a relationship between skew angle and CTS between respective combinations of subsets of the plurality of readers; determining, as a function of the CTS information, a given one of the combinations of subsets of the plurality of readers which provides enhanced read performance among a total number of combinations of subsets of the plurality of readers for each of a plurality of skew angles; and selecting, for subsequent processing by a read channel in the ARMR system, the given one of the combinations of subsets of the plurality of readers determined to provide enhanced read performance for a given one of the plurality of skew angles corresponding to a zone in which the multi-reader head is operating.
 2. The method of claim 1, wherein the CTS information defines a relationship between skew angle and CTS between respective pairs of readers in a plurality of combinations of pairs of readers.
 3. The method of claim 1, further comprising configuring the plurality of readers in the multi-reader head such that at least a subset of the readers are within a CTS range configured to provide prescribed read performance as a function of whether the ARMR system is operating in a multiple-input single-output mode or a multiple-input multiple-output mode.
 4. The method of claim 3, wherein the multi-reader head is configured such that at least a subset of the plurality of readers are within a CTS of 0.3 track pitch (TP) of one another for multiple-input single-output operation, and at least the subset of the readers are within a range of about 0.7 to 0.9 TP of one another for multiple-input multiple-output operation.
 5. The method of claim 1, further comprising locating the multi-reader head over at least one target track of a magnetic storage medium being read based on the CTS information corresponding to the given one of the combinations of subsets of available readers determined to provide enhanced read performance.
 6. The method of claim 1, further comprising configuring at least a subset of the plurality of readers in the multi-reader head such that adjacent readers are located on opposite sides, in a cross-track direction, of a centerline of the multi-reader head, the centerline being oriented in a down-track direction.
 7. The method of claim 1, further comprising storing, for each of at least a subset of the plurality of skew angles, a corresponding one of the combinations of subsets of the plurality of readers determined to provide enhanced read performance among the total number of combinations of subsets of the plurality of readers.
 8. The method of claim 7, wherein selecting the given one of the combinations of subsets of the plurality of readers determined to provide enhanced read performance comprises retrieving one of the stored combinations of subsets of the plurality of readers which provides enhanced read performance as a function of the zone in which the multi-reader head is operating.
 9. The method of claim 1, wherein selecting the given one of the combinations of subsets of the plurality of readers determined to provide enhanced read performance comprises: detecting a zone in which the multi-reader head is operating; and changing the given one of the combinations of subsets of the plurality of readers determined to provide enhanced read performance as a function of the detected zone in which the multi-reader head is operating.
 10. The method of claim 1, wherein determining the given one of the combinations of subsets of the plurality of readers which provides enhanced read performance comprises: determining cross-track separation (CTS) variation as a function of skew angle for each combination of subsets of the plurality of readers in the multi-reader head over a prescribed range of skew angles; and determining which combinations of subsets of the plurality of readers have a CTS that is within a prescribed range of CTS variation for each of at least a subset of skew angles in the prescribed range of skew angles.
 11. The method of claim 10, wherein determining CTS variation for each combination of subsets of the plurality of readers comprises estimating CTS information for the readers from read-back signal processing.
 12. The method of claim 1, further comprising supplying read signals generated by respective readers in the given one of the combinations of subsets of the plurality of readers determined to provide enhanced read performance to corresponding analog front ends in the read channel.
 13. The method of claim 1, wherein selecting the given one of the combinations of subsets of the plurality of readers determined to provide enhanced read performance comprises: determining whether the multi-reader head is to be used in one of a multiple-input single-output mode of operation and a multiple-input multiple-output mode of operation; and selecting a given one of the combinations of subsets of the plurality of readers determined to provide enhanced read performance as a function of the mode of operation of the multi-reader head.
 14. The method of claim 1, further comprising generating a data output signal indicative of a logical state of information read from at least one target track of a magnetic storage medium being read, the data output signal being a function of read signals corresponding to the given one of the combinations of subsets of the plurality of readers determined to provide enhanced read performance for the zone in which the multi-reader head is operating.
 15. The method of claim 14, wherein the data output signal comprises one of a hard decision corresponding to a particular logical state of information read from the at least one target track, or a soft decision corresponding to a probability relating to the particular logical state of the information read from the target track.
 16. An apparatus for enhancing read performance in an array-reader based magnetic recording (ARMR) system, the apparatus comprising: a controller configured to receive, as inputs, a plurality of read signals from a corresponding plurality of readers in a multi-reader head of the ARMR system and to select, as outputs, a subset of the plurality of read signals corresponding to a given one of respective combinations of subsets of the plurality of readers which provides enhanced read performance among a total number of combinations of subsets of the plurality of readers for each of a plurality of skew angles; a plurality of analog front ends, each of the analog front ends being configured to receive a corresponding read signal from the subset of the plurality of read signals output by the controller and to generate an analog signal as a function of the corresponding read signal; a plurality of analog-to-digital converters coupled with the respective plurality of analog front ends, each of the analog-to-digital converters being configured to receive a given one of the analog signals generated by a corresponding one of the plurality of analog front ends and to generate, as a function of the given analog signal, a digital read signal; and a joint equalizer coupled with the plurality of analog-to-digital converters, the joint equalizer being configured to receive the respective digital read signals generated by the plurality of analog-to-digital converters and to generate an equalized output signal.
 17. The apparatus of claim 16, further comprising a detector coupled with the joint equalizer, the detector being configured to generate a data output signal indicative of a logical state of information read from at least one target track of a magnetic storage medium being read, the data output signal being a function of read signals corresponding to the given one of the combinations of subsets of the plurality of readers determined to provide enhanced read performance for a zone in which the multi-reader head is operating.
 18. The apparatus of claim 16, further comprising a zone table coupled with the controller, the zone table being configured to store, for each of at least a subset of the plurality of skew angles, a corresponding one of the combinations of subsets of the plurality of readers determined to provide enhanced read performance among the total number of combinations of subsets of the plurality of readers.
 19. The apparatus of claim 18, wherein the controller is configured to retrieve one of the stored combinations of subsets of the plurality of readers which provides enhanced read performance as a function of a zone in which the multi-reader head is operating.
 20. The apparatus of claim 16, wherein the controller is configured to determine cross-track separation (CTS) variation as a function of skew angle for each combination of subsets of the plurality of readers in the multi-reader head over a prescribed range of skew angles, and to determine which combinations of subsets of the plurality of readers have a CTS that is within a prescribed range of CTS variation for each of at least a subset of skew angles in the prescribed range of skew angles.
 21. The apparatus of claim 20, wherein the controller is configured to determine CTS variation for each combination of subsets of the plurality of readers by estimating CTS information for the readers from read-back signal processing.
 22. The apparatus of claim 16, wherein the controller is configured to detect a zone in which the multi-reader head is operating, and to change the given one of the combinations of subsets of the plurality of readers determined to provide enhanced read performance as a function of the detected zone in which the multi-reader head is operating.
 23. The apparatus of claim 16, wherein the controller is configured to determine whether the multi-reader head is to be used in one of a multiple-input single-output mode of operation and a multiple-input multiple-output mode of operation, and to select the given one of the combinations of subsets of the plurality of readers determined to provide enhanced read performance as a function of the mode of operation of the multi-reader head.
 24. The apparatus of claim 16, wherein at least a portion of the apparatus is fabricated in an integrated circuit.
 25. The apparatus of claim 16, wherein at least a subset of the plurality of analog-to-digital converters are configured to exchange information with one another.
 26. A data storage system, comprising: a plurality of storage devices, wherein at least one of the plurality of storage devices comprises: a multi-reader array head; a controller configured to receive, as inputs, a plurality of read signals from a corresponding plurality of readers in the multi-reader head and to select, as outputs, a subset of the plurality of read signals corresponding to a given one of respective combinations of subsets of the plurality of readers which provides enhanced read performance among a total number of combinations of subsets of the plurality of readers for each of a plurality of skew angles; a plurality of analog front ends, each of the analog front ends being configured to receive a corresponding read signal from the subset of the plurality of read signals output by the controller and to generate an analog signal as a function of the corresponding read signal; a plurality of analog-to-digital converters coupled with the respective plurality of analog front ends, each of the analog-to-digital converters being configured to receive a given one of the analog signals generated by a corresponding one of the plurality of analog front ends and to generate, as a function of the given analog signal, a digital read signal; and a joint equalizer coupled with the plurality of analog-to-digital converters, the joint equalizer being configured to receive the respective digital read signals generated by the plurality of analog-to-digital converters and to generate an equalized output signal. 